In the metal foundry business there is a need for cores that can be placed in the molds which produce voids in the castings as the molten metal is poured into molds. The cores generally are made from a sand and resin mixture that is forced into heated dies. The heat causes the sand-resin mixture to solidify producing the core. Dr. Johan Croning developed the phenolic resin process during WWII in Germany. The Germans gravity fed and hand rammed the resin sand around heated plates and contoured dies to make mortar and artillery shells. The American government brought the process to the United States and promoted it in 1947.
In the 1950""s Dependable foundry made its first machine to pneumatically inject phenolic resin, phenolic flake, and hexa catalyst into heated dies. Hence the first shell core machine was born.
Generally there are two types of cores; solid cores and shell cores which are hollow on the inside.
A variety of machines have been developed to manufacture these cores. In general cores are manufactured in a heated die that is held by a die holder. A sand resin mixture is forced into a fill opening while the fill opening is in an upward position.
When solid cores are made, the entire core hardens. After the core has a final cure, the die holder and die are opened up and the solid core is extracted. After the solid core is extracted, the die holder and die are closed and the cycle is repeated.
When shell cores are made, a sand resin mixture is forced into a fill opening while the fill opening is in an upward position. As the outer layer of resin-sand mixture cures or hardens to a die specified shape and utility thickness, the die holder carriage and die must be rotated so that the fill opening is in a downward position and the die holder is rocked back and forth so that any of the resin-sand that is unhardened will be shaken but of the die. This results in the formation of a hollow or shell core. After the uncured sand is shaken out the die, the die is rotated so that the fill opening is in a 90 degree position (facing the operator). After the core has a final cure, the die holder and die are opened up and the shell core is extracted. After the core is extracted the die holder and die are closed and the cycle is repeated.
There are several different designs of core machines and shell core machines. There are also several methods used to rotate and shake the die holder and die. One design requires the rotating of the die holder carriage and die manually by hand. A second design uses cylinders and pneumatic power to rotate the die holder carriage and die. A third design uses cylinders and hydraulic power to rotate the die holder carriage and die. A fourth design uses an electric motor along with a gear reducer and roller chain to rotate the die holder and die.
The most productive shell core machine has been the pneumatic powered machine. This machine however, has been very problematic. The machine is constantly in need of adjustment.
These machines can produce a wide range of sizes and shapes of shell cores by using different dies in the die holder. Dies for different cores can vary from a few pounds to hundreds of pounds. Sand demand for cores can vary from a few ounces to tens of pounds. Every time a different die is placed into the die holder to make a different part, a lengthy process of changing flow controls and cams and limit switches is required to provide the optimum cycle for producing each different shell core design.
During each short core making cycle the drive system must rotate the heavy die holder carriage, dies, and sand hopper. Because some of the individual components in the drive system are poorly designed, the stresses and strains and impact and inertia changes resulting from rotating the heavy die holder, dies, and sand hopper causes the various components to fail. This results in expensive repairs and much unproductive down time.
Another problem with the pneumatic drive system is that the rotational cycle usually has a jerky motion and does not rotate at a constant high rate of travel through each production cycle.
Another problem with the pneumatic drive system is that the rotational cycle of 270 degrees has a 180 degree portion and a 90 degree portion. The 180 degree portion is where the die front rotates from xe2x80x9ctop dead center to bottom dead centerxe2x80x9d or from zero degrees to 180 degrees. The 90 degree rotation is when the die front rotates from facing the operator at a horizontal to a bottom dead center position. (90 degrees to 180 degrees. The inertia of the 180 degree rotation is greater than the inertia of the 90 degree rotation. The machine can be set for smooth rotation in only one of the rotational portions. In other words, if the machine is set for smooth rotation in the 90 degree portion it will not have smooth rotation in the 180 degree portion and vise versa. The operation manual even states that machine xe2x80x9ccannot be properly set for both conditions!xe2x80x9d
Another problem with the prior art drive system is that at both ends of each 270 degree cycle the drive piston hits the inside end of the piston drive cylinder to bring the heavy die holder carriage assembly to the ending position. Because of the repeated heavy impact between the piston and cylinder at the end of each cycle the drive piston and/or drive cylinder fail often.
It is a primary object of the invention to provide an improved drive system for a shell core machine that overcomes the above problems of the existing prior art.
It is another object of the invention to provide a drive system that is more rugged and more dependable than the existing prior art drive systems.
It is another object of the invention to provide a drive system design that spreads out the stresses and strains and loading and inertia and torsional forces that are the result of rotating the die holder, die, and sand hopper during each core making cycle.
It is another object of the invention to provide a drive system design that uses more than one drive cylinder and piston along with a double ended lever with a drive shaft in a lever center location. This provides a more evenly applied force across all drive components and allows for a greater applied pressure.
It is another object of the invention to provide a drive system that rotates at a consistent high rate of travel, smoothly, through each production cycle rather than the, jerky motion of the prior art drive system.
It is another object of the invention to provide a drive system that uses both air and oil along with a oil/air pressure transducing device or a oil/air pressure transferring device. This smooths out each production cycle. Thus, the jerky motion of the prior art drive system is eliminated.
It is another object of the invention to provide a drive system that provides a cushion at the end of each 270 degree rotation cycle. This minimizes the impact of the drive piston hitting the end of the piston drive cylinder.
It is another object of the invention to provide a drive system that utilizes a combination of air and oil in combination with a metered port or a restricting orifice and check valve to provide a cushion at the end of each piston stroke. This minimizes the impact of the drive piston hitting the end of the piston drive cylinder.
It is another object of the invention to provide a drive system that provides an end of cycle cushion that is adjustable.
It is another object of the invention to provide a drive system with a cushion at the end of each 270 degree rotation cycle that has a long service life.
It is another object of the invention to provide a drive system that provides a more rapid index of die carriage holder and die from start position to blow fill position. This can be up to 50% faster.
It is another object of the invention to provide a drive system that requires very little or no adjustment to compensate for different sizes and weights of different dies that are used to make different cores in the shell core machine.
It is another object of the invention to provide a drive system that requires very little or no adjustment so that there is a smooth rotation through the entire 270 degree rotation; both in clockwise rotations and counterclockwise rotations.